Elevated expression of exogenous RAD51 enhances the CRISPR/Cas9-mediated genome editing efficiency

Synergistic combination of RAD51-SCR7 improves CRISPR-Cas9 genome editing efficiency by preventing R-loop accumulation

CRISPR-Cas9 has emerged as a powerful tool for genome editing. However, Cas9 genome editing faces challenges, including low efficiency and off-target effects. Here, we report that combined treatment with RAD51, a key factor in homologous recombination, and SCR7, a DNA ligase IV small-molecule inhibitor, enhances CRISPR-Cas9-mediated genome-editing efficiency in human embryonic kidney 293T and human induced pluripotent stem cells, as confirmed by cyro- transmission electron microscopy and functional analyses. First, our findings reveal the crucial role of RAD51 in homologous recombination (HR)-mediated DNA repair process. Elevated levels of exogenous RAD51 promote a post-replication step via single-strand DNA gap repair process, ensuring the completion of DNA replication. Second, using the all-in-one CRISPR-Cas9-RAD51 system, highly expressed RAD51 improved the multiple endogenous gene knockin/knockout efficiency and insertion/deletion (InDel) mutation by activating the HR-based repair pathway in concert with SCR7. Sanger sequencing shows distinct outcomes for RAD51-SCR7 in the ratio of InDel mutations in multiple genome sites. Third, RAD51-SCR7 combination can induce efficient R-loop resolution and DNA repair by enhanced HR process, which leads to DNA replication stalling and thus is advantageous to CRISPR-Cas9-based stable genome editing. Our study suggests promising applications in genome editing by enhancing CRISPR-Cas9 efficiency through RAD51 and SCR7, offering potential advancements in biotechnology and therapeutics.

Caffeine enhances chemosensitivity to irinotecan in the treatment of colorectal cancer

BACKGROUND

Colorectal cancer (CRC) is one of the most common types of cancer. This disease arises from gene mutations and epigenetic alterations that transform colonic epithelial cells into colon adenocarcinoma cells, which display a unique gene expression pattern compared to normal cells. Specifically, CRC cells exhibit significantly higher expression levels of genes involved in DNA repair or replication, which is attributed to the accumulation of DNA breakage resulting from rapid cell cycle progression.

PURPOSE

This study aimed to investigate the in vivo effects of caffeine on CRC cells and evaluate its impact on the sensitivity of these cells to irinotecan, a topoisomerase I inhibitor widely used for CRC treatment.

METHODS

Two CRC cell lines, HCT116 and HT29, were treated with irinotecan and caffeine. Western blot analysis assessed protein expression levels in caffeine/irinotecan-treated CRC cells. Immunofluorescence staining determined protein localization, measured DNA breaks, and explored the effects of DNA damage reagents during cell cycle progression and flow cytometry analysis was used to measure cell viability. Fiber assays investigated DNA synthesis in DNA-damaged cells during S-phase, while the comet assay assessed DNA fragmentation caused by DNA breaks.

RESULTS

Our findings demonstrated that the combination of irinotecan and caffeine exhibits a synergistic effect in suppressing CRC cell proliferation and inducing cell death. Compared to treatment with only irinotecan or caffeine, the combined irinotecan and caffeine treatment was more effective in inducing DNA lesions by displacing RAD51 from DNA break sites and inhibiting DNA repair progression, leading to cell cycle arrest. This combination also resulted in more severe effects, including DNA fragmentation and mitotic catastrophe.

CONCLUSION

Caffeine could enhance the effectiveness of an existing drug for CRC treatment despite having little impact on the cell survival rate of CRC cells. Our findings suggest that the beneficial adjuvant effects of caffeine may not only be applicable to CRC but also to various other types of cancers at different stages of development.